tests/boot_linux_console: add extract_from_rpm method

tests/boot_linux_console: add extract_from_rpm method

Add a method to extract a specified file from an RPM to the test's
working directory and return the path to the extracted file.

Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <1580914565-19675-5-git-send-email-liam.merwick@oracle.com>
[PMD: Rebased]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>